In general, a fuel pump such as an in-tank type fuel pump, which is accommodated in a fuel tank, is required to being downsized in view of a mounting space for the fuel pump. According to JP-B2-2776304, a fuel pump includes a commutator, which is in a flat disc shape, brushes, and an armature. Brushes are provided on the opposite side of the commutator with respect to the armature. In this structure, the outer diameter of the fuel pump can be reduced.
According to JP-A-2001-352731, a fuel pump includes an armature including a rotor core. The rotor core has the outer circumferential peripheries in one axial end, and the outer circumferential peripheries are bent. In this structure, magnetic flux formed between permanent magnets, which are provided on the radially outer side of the armature, and the rotor core can be enhanced without axially extending the armature. That is, torque produced using the motor portion can be enhanced in the case where the axial length of the motor portion of the fuel pump is the same. Alternatively, the axial length of the motor portion can be reduced, so that the axial length of the fuel pump can be downsized, in the case where torque required to the motor portion is the same.
Here, JP-A-2001-352731 discloses a commutator in a cylindrical shape. This commutator is downsized, so that brushes can be provided to the radially outer side of the commutator. Collar portions are provided to a rotor core by bending the outer circumferential peripheries of one axial end of the rotor core. The outer circumferential periphery of the cylindrical commutator and the collar portions define a space therebetween. When the commutator is in a cylindrical shape, this space can be readily secured, and wires can be wound to form coils in this space.
A fuel pump can be downsized by combining the disc-shape commutator in JP-B2-2776304 and the rotor core, which has the bent outer circumferential peripheries in the axial end, in JP-A-2001-352731. However, in this combined structure, it is hard to secure the space, in which wires are wound to form coils, between the commutator and the rotor core. The distance between the commutator and the rotor core may be axially extended for securing a space, in which wires are wound to form coils, between the disc-shaped commutator and the rotor core having the bent outer circumferential periphery. However, when the distance between the commutator and the rotor core is axially extended, the fuel pump is axially elongated.
An armature includes a rotor core and coils, which is formed by wining wires on the rotor core. In general, a resin material is charged in an armature and a commutator for reducing resistance against rotation of a motor portion in a furl pump. Furthermore, electrically connecting portions between coils, windings of the coils, and terminals can be protected from corrosion by charging the resin material in a furl pump. In JP-A-H06-122133, an armature and a commutator are provided in molding dies, and a resin material is charged into the molding dies.
The armature includes a rotation shaft, which serves as a rotation axis, assembled by, for example, being press-inserted into a rotor core of the armature. In this structure, when the rotor core is axially applied with molding pressure of the resin material charged into the molding dies, the rotor core may be displaced axially relative to the rotation shaft. For example, the rotation shaft is press-inserted into the rotor core to secure therebetween high connecting strength such as 980 N (100 kgf). That is, in this case, it is necessary to apply force of about 980 N for displacing the rotor core relative to the rotation shaft. However, even in this case, when molding pressure is applied from axially one side to the rotor core being 25 mm in diameter, allowable molding pressure, by which the rotor core is not displaced axially relative to the rotation shaft, is about 2 MPa. In general, a resin injection molding apparatus is capable of applying molding pressure greater than ten-times of the allowable molding pressure. Accordingly, the rotor core may be displaced relative to the rotation shaft when being applied with the molding pressure in a resin injection molding apparatus.